If a wavy distortion, so-called “surface distortion”, exists on a surface of industrial products having specular or semi-specular surfaces, such as press-formed and coated vehicle outer panels, coated architectural wall panels, or flat glass mirrors, a reflected background image looks significantly distorted due to the principle of “optical lever” no matter how small the distortion is. This considerably defaces the appearance of the industrial products and inflicts great damage on the quality thereof.
The above-described distortion is caused at any steps of performing a series of processing operations, such as press-forming, assembling, and coating of a metal plate. During the press-forming, a surface of a press-formed product may deform due to the elastic deformation after the mold-releasing, and a distortion is possibly caused. Additionally, when an extraneous matter, such as iron powder, attaches to a press die, a distortion may be caused on the press-formed product. In addition, when a crack or a wrinkle is caused on a part of the press-formed product in the course of the press-forming, the tension of the product changes, which induces a distortion. During the assembling, caulking or welding may cause a distortion. During the coating, thermal deflection and coating unevenness due to baking, and attachment of an extraneous matter may cause a distortion.
Accordingly, a technique for quantitatively measuring surface-distortion distribution has been desired at sites of product development and manufacturing, such as evaluation, building of the quality, and quality inspection of materials of these industrial products.
However, it is extremely difficult to perform a quantitative shape measurement all over a surface of a target to measure the ruggedness of approximately 10 μm to 100 μm on the surface of the target of several hundreds millimeters to several meters in size. Hitherto, a method for determining distribution of small shape distortions by performing x-y scanning on a surface of a target using a non-contact rangefinder represented by a laser displacement gauge has been known. However, the method takes a lot of time to perform the measurement, and is not a practical method.
On the other hand, hitherto, a method for evaluating a surface distortion on the basis of the degree of deformation utilizing a phenomenon that an mirror image of a background stripe pattern or a background checker board pattern reflected in a surface of a target looks distorted due to the surface distortion has been known as a method for performing quantitative pattern observation of a surface distortion.
A method disclosed in Patent Document 1 is one of qualitative surface-distortion observation methods that mainly target at mirror-coated large architectural panels. The method attempts to determine the degree of surface distortion on the basis of a magnitude relation between a line-width and a line-interval of a predetermined line included in several kinds of stripe patterns having different line-widths and line-intervals reflected in the panel and thresholds therefor.
In addition, a method disclosed in Patent Document 2, Patent Document 3, Patent Document 4, or Patent Document 5 has been suggested mainly as a method for observing a distortion on and inside a glass. The method attempts to evaluate the distortion on the basis of a degree of deformation, a curvature, a line-width, and a line-interval of a reflected image reflected on a surface of the measurement-target glass or a transmitted image inside the glass by observing the reflected image or the transmitted image of a stripe pattern or a checker board pattern.
On the other hand, Patent Document 6, Patent Document 7, or Patent Document 8 advances the above-described observation methods by one step, and discloses an attempt to quantify this distortion. These methods attempt to quantify the distortion by focusing on a fact that a contrast or a phase shift of a stripe pattern or a checker board pattern, or a generated moiré fringe changes depending on the degree of distortion.
In addition, Patent Document 9 discloses a method for sensitively detecting a small rugged defect on a semi-specular coated surface of a body of a vehicle, although the object of the method is more or less different from the surface-distortion measurement. In this method, a slit diffusion illumination light is irradiated, and a timing at which a mirror image of the slit reflected in the surface of the measurement target passes each point on the surface of the target is determined by image synthesis. The method attempts to detect a defect on the basis of a partial distortion of a timing pattern resulting from the small rugged defect. This method can be transferred to observation of surface distortions, and provides a robust observation method for shapes of a target.
Patent Document 10 discloses a method for determining fine ruggedness distribution. In the method, a plurality of kinds of stripe array patterns used in the binary-coded pattern projection method are sequentially projected from a point-source light. The projected patterns are photographed, and the photographed images are processed to determine coarse ruggedness distribution. Processing for scanning slits, parallel to the one pair of the stripes, in a direction orthogonal to a stripe-extending direction in a range covered with one pair of light and shade stripes in one stripe array pattern from the stripe array patterns is simultaneously performed on all pairs of stripes. During the scanning of slits, coordinate values of positions of the slit-scanning at the time that each pixel shows the maximum brightness are captured all over the image. Ultimately, the coarse ruggedness distribution determined by sequentially displaying the above-described stripe array patterns is complemented by the fine ruggedness distribution determined by scanning the slits, thereby determining the overall fine ruggedness distribution.
Here, the binary-coded pattern projection method is a position recognition method for sequentially projecting a plurality of kinds of stripe array patterns, temporarily recognizing a position as a corresponding binary number on the basis of a pattern whose light and shade are switched according to the position, and ultimately recognizing the position as a decimal number after converting the binary number into the decimal number as shown in FIG. 15. The stripe array pattern may be, for example, a stripe array pattern having light and shade alternately arranged at 2n equally divided sections.
For example, FIG. 15 shows a state in which first to third-order patterns are sequentially projected onto a reference surface 20 from a point-source light 15. A light-and-shade pattern displayed on a leftmost section corresponding to “7”, among positions represented by decimal numbers corresponding to n-th positions from the left of sections shown in the bottom, is recognized as a corresponding binary number, such as “1” for light in the first-order pattern, “1” for light in the second-order pattern, and “1” for light in the third-order patter, thus the position is recognized as 22×1+22-1×1+22-2×1=7. Similarly, a light-and-shade pattern displayed on the second section from the left corresponding to “6” among the positions represented by decimal numbers corresponding to the sections shown in the bottom is recognized as a corresponding binary number, such as “1” for light in the first-order pattern, “1” for light in the second-order pattern, and “0” for shade in the third-order pattern, thus the position is recognized as 22×1+22-1×1+22-2×0=6. Likewise, a light-and-shade pattern displayed on the third section from the left corresponding to “5” among the positions represented by decimal numbers corresponding to the sections shown in the bottom is recognized as a corresponding binary number, such as “1” for light in the first-order pattern, “0” for shade in the second-order pattern, and “1” for light in the third-order pattern, thus the position is recognized as 22×1+22-1×0+22-2×1=5. That is how the position is recognized.
The cited Patent Documents are collectively listed below.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-153420
Patent Document 2: Japanese Unexamined Patent Application Publication No. 60-119404
Patent Document 3: Japanese Unexamined Patent Application Publication No. 1-165907
Patent Document 4: Japanese Unexamined Patent Application Publication No. 3-135704
Patent Document 5: Japanese Unexamined Patent Application Publication No. 3-199946
Patent Document 6: Japanese Unexamined Patent Application Publication No. 7-20059
Patent Document 7: Japanese Unexamined Patent Application Publication No. 8-220021
Patent Document 8: Japanese Unexamined Patent Application Publication No. 2004-251878
Patent Document 9: Japanese Unexamined Patent Application Publication No. 2002-22665
Patent Document 10: Japanese Unexamined Patent Application Publication No. 2005-3409
However, techniques disclosed in Patent Documents 2 to 5 only visualize the distortion, and does not guarantee quantification of measured values.
In addition, in techniques disclosed in Patent Documents 6 to 8, the measurement result is likely to be affected by the light-and-shade of the projected stripe pattern or checker board pattern. Additionally, an observable area is limited to an area near the edge of the light-and-shade portion of the pattern or a spatial resolution is limited due to averaging. Accordingly, the limitation is imposed on the efficiency.
Furthermore, in a technique disclosed in Patent Document 9, a problem remains in that a time required for measurement is long since a mirror image is scanned with one slit and in that quantitative evaluation equation between the timing lags and the degree of surface distortion is not established.
Moreover, in a technique disclosed in Patent Document 10, values of coordinates in the slit-scanning direction at the time that each pixel shows the maximum brightness are determined by measuring an angle θ shown in FIG. 15. Thus, as a matter of limitation on resolution of the angle θ, it is possible to easily perform quantitative measurement of ruggedness of approximately several millimeters, such as, for example, ups and downs of a person's face. However, it is impossible to perform quantitative measurement of surface-distortion distribution equivalent to small ruggedness of approximately several tens micrometers on a specular surface or semi-specular surface, such as, for example, a surface of a vehicle outer panel.
In addition, when inspection of surface quality-defects resulting from a surface distortion is performed in each of metal-plate processing steps of performing at least one of press-forming, component mounting, assembling, coating, heat treatment, and inspection of a finished product, it is necessary to inspect the product moving on the manufacturing line at a high-speed. However, conventional techniques cannot cope with the speed of product moving on the manufacturing line, and it is impossible to perform inline inspection.
In view of these problems in the related art, it is an object of the present invention to provide surface-distortion measuring device and method capable of quantitatively, rapidly, and highly accurately measuring and evaluating surface-distortion distribution at all of observable points on a specular or semi-specular surface of a measurement target.